Drive power transmission device, image forming apparatus and process cartridge

ABSTRACT

A transmission mechanism for transmitting rotation of a driving source in a main body to an object mounted on the main body for receiving the rotation, the transmission mechanism comprising a plurality of couplings provided at different positions along an axial direction of a rotating axis; wherein each of the couplings comprises, a male coupling member having a plurality of convex elements provided at an identical internal on an outer circumferential surface of the rotating axis; and a female coupling member having a plurality of concave elements for engaging with the convex elements.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a drive power transmissiondevice and an image forming apparatus equipped with the drive powertransmission device, and in particular, to a drive power transmissiondevice which transmits a rotation drive force coming from a drivingsource to a detachable driven member, an image forming apparatusequipped with the drive power transmission device and to a processcartridge.

[0002] For example, in many image forming apparatuses forming imagesthrough an electrophotographic system, a photoreceptor and a developingdevice are detachably provided on the image forming apparatus main body.As a detachable component to be provided detachably, there are given onewherein a photoreceptor and an individual developing device are unitizedintegrally, one wherein a photoreceptor and a developing device areunited as a unit and common one wherein components around aphotoreceptor such as a charging device and a cleaning device inaddition to the aforesaid photoreceptor and developing device are formedas a unit to be the detachable component that is called a processcartridge.

[0003] The detachable component of this kind includes those which rotatein the course of image forming such as a photoreceptor and a developingsleeve, and these rotary components are connected to a driving source onthe image forming apparatus main body then they are mounted.

[0004] Incidentally, a drive system that drives rotary components suchas a photoreceptor and a developing sleeve is required to be one whereinan occurrence of rotational irregularity and a vibration is strictlyrepressed. The reason for this is that image quality is easily affectedby rotational irregularity and a vibration to the utmost extent. On theother hand, when driving components that can be mounted and dismounted,rotational irregularity and a vibration are easily caused. To satisfythese antinomic requirements, there have been made various inventions.

[0005] In TOKKAIHEI 4-15315, there is suggested to use a universal jointwherein rotatable link mechanisms in a plurality of steps are combined.

[0006] In JiKKAIHEI 5-25453, TOKKAIHEI 8-6368, TOKKAIHEI 8-6456 andTOKKAIHEI 8-6457, there is described to use a universal joint of apin-coupling type.

[0007] In TOKKAIHEI 8-220938, there is described that a spline-couplingin one step is used. Further, in TOKKAIHEI 9-66637, there is describedthat a coupling portion is provided on each of an inner circumferentialsurface and an outer circumferential surface of an elastic member.

[0008] In the conventional examples stated above, there is a problemthat rotational irregularity and vibration both generated whiledetachable components are driven to rotate cannot be preventedsufficiently.

[0009] It is considered that the causes for occurrence of the rotationalirregularity and vibration both generated while detachable componentsare driven to rotate lie in the following points.

[0010] In the drive system wherein connection is cut by dismounting, itis unavoidable to a certain extent that an axis of a driving side isdeviated from that of a driven side. Because of this deviation, adeviating force in addition to rotational force is applied to a drivenshaft in the course of rotation, and thereby, the rotationalirregularity and vibration are caused. Each of a pin type universaljoint and a one-step spline coupling is one wherein a driving shaft anda driven shaft are connected with a coupling having a buffer effect torepress an occurrence of rotational irregularity and vibration even whenthe driving shaft is deviated from the driven shaft, but it has beenconfirmed that an effect of the repression is not sufficient.

[0011] In the conventional technology stated above, therefore, atolerance for the deviation between the driving shaft and the drivenshaft is small, which causes a problem in manufacturing and a costincrease.

[0012] Further, since a tolerance for the deviation between the drivingshaft and the driven shaft is small, workability for mounting anddismounting is lowered. Further, in the case of a mechanism requiringfixing with a screw for mounting, workability for mounting anddismounting is further lowered. An object of the invention is to solvethe problem stated above in the driving system wherein a driven shaftcan easily be mounted on a driving shaft.

SUMMARY OF THE INVENTION

[0013] Accordingly, to overcome the cited shortcomings, theabovementioned object of the present invention can be attained bytransmission mechanisms, process cartridges and image-forming apparatusdescribed as follow.

[0014] (1) A transmission mechanism for transmitting rotation of adriving source in a main body to an object mounted on the main body forreceiving the rotation, the transmission mechanism comprising: aplurality of couplings provided at different positions along an axialdirection of a rotating axis; wherein each of the couplings comprises, amale coupling member having a plurality of convex elements provided atan identical interval on an outer circumferential surface of therotating axis; and a female coupling member having a plurality ofconcave elements for engaging with the convex elements.

[0015] (2) The transmission mechanism of item 1, wherein the object isdetachable from the main body.

[0016] (3) The transmission mechanism of item 1, wherein the malecoupling member provides more than four convex elements and the femalecoupling member provides more than four concave elements.

[0017] (4) The transmission mechanism of item 1, wherein each convexelements has an affecting surface arranged on a plane including therotating axis, and wherein the affecting surface transmits a drivingforce to one of the concave elements.

[0018] (5) The transmission mechanism of item 1, wherein each ofstresses of the couplings is different.

[0019] (6) The transmission mechanism of item 1, wherein a top corner ofan affecting surface of each the convex elements is chamfered, andwherein the affecting surface transmits a driving force to one of theconcave elements.

[0020] (7) The transmission mechanism of item 1, wherein each of theconvex elements has an affecting surface transmitting a driving force toone of the concave elements, and wherein a phase of affecting surfacesof one of the couplings is different from a phase of affecting surfacesof another one of the couplings.

[0021] (8) A transmission mechanism for transmitting rotation of adriving source in a main body to a detachable body detachably mounted onthe main body, the transmission mechanism comprising: a driving couplingmember provided in the main body, wherein the driving coupling member isrotated by the driving source; an intermediate member having a firstcoupling member and a second coupling member, both of which are providedat different positions along an axial direction of a rotating axis; anda driven coupling member provided in the detachable body; wherein thedriving coupling member couples with the first coupling member and thedriven coupling member couples with the second coupling member so thatthe rotation of the driving source is transmitted from the drivingcoupling member to the driven coupling member through the intermediatemember, and wherein each of the first coupling member and the secondcoupling member is either a male coupling member or a female couplingmember.

[0022] (9) The transmission mechanism of item 8, wherein the drivingcoupling member loosely couples with the first coupling member, and thedriven coupling member also loosely couples with the second couplingmember.

[0023] (10) The transmission mechanism of item 9, wherein each of playsbetween the driving coupling member and the first coupling member andbetween the driven coupling member and the second coupling member ismore than 0.08 mm.

[0024] (11) The transmission mechanism of item 10, wherein each of theplays is less than 1.00 mm.

[0025] (12) The transmission mechanism of item 8, wherein the malecoupling member has more than four convex elements, and the femalecoupling member has more than four concave elements.

[0026] (13) The transmission mechanism of item 8, wherein a first stressbetween the driving coupling member and the first coupling member isdifferent from a second stress between the second coupling member andthe driven coupling member.

[0027] (14) The transmission mechanism of item 13, wherein the firststress is less than the second stress in case that the intermediatemember holds to the driving coupling member, and the second stress isless than the first stress in case that the intermediate member holds tothe driven coupling member.

[0028] (15) The transmission mechanism of item 8, wherein a top cornerof an affecting surface of the convex element is chamfered, and whereinthe affecting surface transmits a driving force to a concave elementcoupling with the convex element.

[0029] (16) The transmission mechanism of item 8, wherein the first andsecond coupling members have male coupling members having a plurality ofconvex elements positioned at an identical interval on an outercircumferential surface of the rotating axis, wherein each the convexelements has an affecting surface transmitting a driving force to aconcave element coupling with the convex element, and wherein a phase ofaffecting surfaces of one of the male coupling members is different froma phase of affecting surfaces of the other of the male coupling members.

[0030] (17) The transmission mechanism of item 8, wherein the malecoupling member has a plurality of convex elements and the femalecoupling member has a plurality of concave elements, and wherein anumber of the convex or the concave elements of the first intermediatecoupling member accords with a number of the convex or the concaveelements of the second intermediate coupling member.

[0031] (18) The transmission mechanism of item 8, wherein the firstcoupling member or the second coupling member is coupled with either thedriving coupling member or the driven coupling member so that theintermediate member has a variable angle to the rotating axis in casethat the detachable body is detached from the main body.

[0032] (19) A transmission mechanism for transmitting rotation of adriving source in a main body to a detachable body detachably mounted onthe main body, the transmission mechanism comprising: a driving couplingmember provided in the main body, wherein the driving coupling member isrotated by the driving source; an intermediate member having a firstcoupling member and a second coupling member, both of which are providedat different positions along an axial direction of a rotating axis; anda driven coupling member provided in the detachable body; wherein thedriving coupling member couples with the first coupling member and thedriven coupling member couples with the second coupling member so thatthe rotation of the driving source is transmitted from the drivingcoupling member to the driven coupling member through the intermediatemember, and wherein the first coupling member or the second couplingmember is coupled with either the driving coupling member or the drivencoupling member so that the intermediate member has a variable angle tothe rotating axis in case that the detachable body is detached from themain body.

[0033] (20) The transmission mechanism of item 19, wherein each of thefirst coupling member and the second coupling member has either a malecoupling member which has a plurality of convex elements positioned atan identical interval on an outer circumferential surface of therotating axis or a female coupling member which has a plurality ofconcave elements for engaging with the plurality of convex elements.

[0034] (21) A transmission mechanism for transmitting rotation of adriving source in a main body to a detachable body detachably mounted onthe main body, the transmission mechanism comprising: a male couplingmember provided in either the main body or the detachable body, whereinthe male coupling member has a plurality of convex elements provided atan identical interval on an outer circumferential surface of a rotatingaxis; and a female coupling member provided in the other of either themain body or the detachable body, wherein the female coupling member hasa plurality of concave elements for engaging with the convex elements;wherein one of the convex elements and the concave elements provided inthe main body have affecting surfaces for transmitting a driving forceto the other of the convex elements and the concave elements provided inthe detachable body, and wherein each top corner of the affectingsurfaces is chamfered.

[0035] (22) A process cartridge, detachably mounted on a main body of animage forming apparatus, to which rotation of a driving source, locatedat the main body, is transmitted, the process cartridge comprising: anintermediate member having a first coupling member coupled with adriving coupling member rotated by the driving source, and having asecond coupling member, wherein the first and second coupling membersare provided at different positions along an axial direction of arotating axis; a driven coupling member coupled with the second couplingmember, wherein the rotation of the driving source is transmitted fromthe driving coupling member to the driven coupling member through theintermediate member; wherein each of the first coupling member and thesecond coupling member is either a male coupling member or a femalecoupling member.

[0036] (23) A process cartridge, detachably mounted on a main body of animage forming apparatus, to which rotation of a driving source, locatedat the main body, is transmitted, the process cartridge comprising: anintermediate member having a first coupling member coupled with adriving coupling member rotated by the driving source, and having asecond coupling member; a driven coupling member coupled with the secondcoupling member, wherein the rotation of the driving source istransmitted from the driving coupling member to the driven couplingmember through the intermediate member; wherein the second couplingmember is coupled with the driven coupling member so that theintermediate member has a variable angle to a rotating axis in case thatthe process cartridge is detached from the main body.

[0037] (24) An image forming apparatus comprising: a main body providinga driving source; an object mounted on the main body; a transmissionmechanism for transmitting rotation of the driving source from the mainbody to the object, wherein the transmission mechanism has a pluralityof couplings provided at different positions along an axial direction ofa rotating axis, and wherein each of the couplings comprises, a malecoupling member having a plurality of convex elements provided at anidentical interval on an outer circumferential surface of the rotatingaxis; and a female coupling member having a plurality of concaveelements for engaging with the convex elements.

[0038] (25) The image forming apparatus of item 24, wherein the objectcomprises a process cartridge detachably mounted on the main body.

[0039] (26) An image forming apparatus comprising: a main body providinga driving source; a detachable body detachably mounted on the main body;a transmission mechanism for transmitting rotation of a driving sourcefrom the main body to the detachable body, wherein the transmissionmechanism comprises, a driving coupling member provided in the mainbody, and rotated by the driving source; an intermediate member having afirst coupling member and a second coupling member, both of which areprovided at different positions along an axial direction of a rotatingaxis; and a driven coupling member provided in the detachable body;wherein the driving coupling member couples with the first couplingmember and the driven coupling member couples with the second couplingmember so that the rotation of the driving source is transmitted fromthe driving coupling member to the driven coupling member through theintermediate member; wherein each of the first coupling member and thesecond coupling member is either a male coupling member or a femalecoupling member.

[0040] (27) The image forming apparatus of item 26, wherein thedetachable body comprises a process cartridge.

[0041] Further, to overcome the abovementioned problems, othertransmission mechanisms, process cartridges and image-forming apparatus,embodied in the present invention, will be described as follow:

[0042] Structure 1

[0043] A drive power transmission device that transmits a rotation of adriving source from the main body side to a rotated member that can bemounted on and dismounted from a main body, wherein there are provided aplurality of couplings each being composed of a male coupling sectioncomposed of a plurality of convex sections provided at regular intervalson the circumferential surface whose center is each rotary shaft and ofa female coupling section composed of concave sections which engage withthe aforesaid plural convex sections, and each of the plural couplingsis provided to be shifted in the axial direction.

[0044] Structure 2

[0045] A drive power transmission device that transmits a rotation of adriving source from the main body side to a rotated member that can bemounted on and dismounted from a main body, wherein there are provided adriving side member that is provided on the main body side and has adriving side coupling section and transmits a rotation of the drivingsource, an intermediate member having a first intermediate couplingsection engaging with the driving side coupling section and having asecond intermediate coupling section and transmitting a rotation of thedriving source through the driving side member and a driven side memberthat is provided on the rotated member side and has a driven sidecoupling section engaging with the second intermediate coupling sectionand transmits a rotation of the driving source to the rotated memberstated above through the driving side member and the intermediatemember, and one of the driving side coupling section and the firstintermediate coupling section and one of the second intermediatecoupling section and the driven side coupling section constitute a malecoupling section composed of plural convex portions provided at regularintervals on a circumferential surface whose center is each rotaryshaft, while, the other of the driving side coupling section and thefirst intermediate coupling section and the other of the secondintermediate coupling section and the driven side coupling sectionconstitute a female coupling section composed of plural concave portionsengaging with the plural convex portions, thus, the male coupling andthe female coupling can be engaged with each other loosely anddetachably.

[0046] Structure 3

[0047] The drive power transmission device according to Structure 2,wherein an amount of a play between the male coupling and the femalecoupling both are to be engaged with each other loosely is not less than0.08 mm.

[0048] Structure 4

[0049] The drive power transmission device according to either one ofStructures 1-3, wherein four or more of the convex portions and four ormore of the concave portions are provided.

[0050] Structure 5

[0051] A drive power transmission device that transmits a rotation of adriving source from the main body side to a rotated member that can bemounted on and dismounted from a main body, wherein there are provided adriving side member that is provided on the main body side and has adriving side coupling section and transmits a rotation of the drivingsource, an intermediate member having a first intermediate couplingsection engaging with the driving side coupling section and having asecond intermediate coupling section and transmitting a rotation of thedriving source through the driving side member and a driven side memberthat is provided on the rotated member side and has a driven sidecoupling section engaging with the second intermediate coupling sectionand transmits a rotation of the driving source to the rotated memberstated above through the driving side member and the intermediatemember, and the intermediate member is supported so that it may bedisplaced to the one side of the driving side member or the driven sidemember when the rotated member is removed from the main body side.

[0052] Structure 6

[0053] The drive power transmission device according to either one ofStructures 2-5, wherein one of the driving side coupling section and thefirst intermediate coupling section and one of the second intermediatecoupling section and the driven side coupling section constitute a malecoupling section composed of plural convex portions provided at regularintervals on a circumferential surface whose center is each rotaryshaft, while, the other of the driving side coupling section and thefirst intermediate coupling section and the other of the secondintermediate coupling section and the driven side coupling sectionconstitute a female coupling section composed of plural concave portionsengaging with the plural convex portions.

[0054] Structure 7

[0055] The drive power transmission device according to either one ofStructures 1-6, wherein the operating surface of each coupling sectionis provided on the plane including the rotary axis.

[0056] Structure 8

[0057] The drive power transmission device according to either one ofStructures 1-7, wherein the safety factor of coupling between thedriving side coupling and the first intermediate coupling is differentfrom that of coupling between the second intermediate coupling and thedriven side coupling.

[0058] Structure 9

[0059] The drive power transmission device according to Structure 8,wherein the safety factor of coupling between the driving side memberholding the intermediate member so that the intermediate member may bedisplaced and the intermediate member or between the driven side memberand the intermediate member is smaller than that of the other coupling.

[0060] Structure 10

[0061] The drive power transmission device according to either one ofStructures 1-9, wherein the operating surface side of the tip of thecoupling section stated above is chamfered.

[0062] Structure 11

[0063] The drive power transmission device according to either one ofStructures 1-10, wherein an operating surface with the driving sidemember in the intermediate member is deviated in terms of phase from anoperating surface with the driven side member in the intermediatemember.

[0064] Structure 12

[0065] The drive power transmission device according to either one ofStructures 1-11, wherein the number of teeth of the first intermediatecoupling section is the same as that of the second intermediate couplingsection.

[0066] Structure 13

[0067] The drive power transmission device according to either one ofStructures 2-12, wherein a position of coupling between the driving sidemember and the intermediate member is deviated in the axial directionfrom that of coupling between the intermediate member and the drivenside member.

[0068] Structure 14

[0069] A drive power transmission device that transmits a rotation of adriving source from the main body side to a rotated member that can bemounted on and dismounted from a main body, wherein a coupling isprovided between a driving source on the main body side and the rotatedmember, and the coupling is composed of a male coupling section that iscomposed of a plurality of convex portions provided at regular intervalson a circumferential surface whose center is the rotational axis and ofa female coupling section that is composed of a plurality of concaveportions which engage with the plural convex portions, and an operatingsurface of a tip of the convex portion or of the concave portion of thecoupling section on at least the driving source is chamfered.

[0070] Structure 15

[0071] An image forming apparatus of an electrophotographic typeequipped with the drive power transmission device described in eitherone of the Structures 1-14, wherein the aforesaid main body side is theimage forming apparatus main body side, and the rotated member is amember in a cartridge provided detachably on the image forming apparatusmain body.

[0072] Structure 16

[0073] The image forming apparatus according to Structure 15, whereinthe unit stated above is at least one of a developing unit that forms atoner image, an image forming body unit on which a toner image isformed, and an image holding unit onto which the toner image formed onthe image forming body is transferred to be held.

[0074] Structure 17

[0075] The image forming apparatus according to Structure 15, whereinthe developing unit has a plurality of rotated members and is providedwith a plurality of driving devices.

[0076] Structure 18

[0077] The image forming apparatus according to Structure 15, whereinthe developing unit has a plurality of developing devices and forms acolor image.

[0078] Structure 19

[0079] A process cartridge capable of being mounted on and dismountedfrom an image forming apparatus main body and having a rotated member,wherein there are provided an intermediate member having a firstintermediate coupling section capable of engaging with a driving sidecoupling section connected to a driving source provided on a main bodyand a second intermediate coupling section, and to which a rotation ofthe driving source is transmitted and a driven side member that has adriven side coupling section engaging with the second intermediatecoupling and transmits a rotation of the driving source to the rotatedmember through the intermediate member, and one of the driving sidecoupling section and the first intermediate coupling section, and one ofthe second intermediate coupling section and the driven side couplingsection constitute a male coupling section composed of a plurality ofconvex portions provided at regular intervals to extend in the axialdirection on a circumferential surface whose center is each rotationalaxis, while the other of the driving side coupling section and the firstintermediate coupling section and the other of the second intermediatecoupling section and the driven side coupling section constitute afemale coupling section composed of a plurality of concave portionsengaging with the convex portions, and the first intermediate couplingsection and the second intermediate coupling section are deviated fromeach other in the axial direction.

[0080] Structure 20

[0081] A process cartridge that is capable of being mounted on anddismounted from an image forming apparatus main body and has a rotatedmember, wherein there are provided an intermediate member having a firstintermediate coupling section capable of engaging with a driving sidecoupling section connected to a driving source provided on a main bodyand a second intermediate coupling section, and to which a rotation ofthe driving source is transmitted and a driven side member that has adriven side coupling section engaging with the second intermediatecoupling and transmits a rotation of the driving source to the rotatedmember through the intermediate member, and one of the driving sidecoupling section and the first intermediate coupling section, and one ofthe second intermediate coupling section and the driven side couplingsection constitute a male coupling section composed of a plurality ofconvex portions provided at regular intervals to extend in the axialdirection on a circumferential surface whose center is each rotationalaxis, while the other of the driving side coupling section and the firstintermediate coupling section and the other of the second intermediatecoupling section and the driven side coupling section constitute afemale coupling section composed of a plurality of concave portionsengaging with the convex portions, and the male coupling section and thefemale coupling section are loose-fitted each other to be capable ofbeing engaged with each other.

[0082] Structure 21

[0083] A process cartridge that is capable of being mounted on anddismounted from an image forming apparatus main body and has a rotatedmember, wherein there are provided an intermediate member having a firstintermediate coupling section capable of engaging with a driving sidecoupling section connected to a driving source provided on a main bodyand a second intermediate coupling section, and to which a rotation ofthe driving source is transmitted and a driven side member that has adriven side coupling section engaging with the second intermediatecoupling and transmits a rotation of the driving source to the rotatedmember through the intermediate member, and the intermediate member isheld on the driven side member so that the intermediate member may bedisplaced.

[0084] Structure 22

[0085] A process cartridge that is capable of being mounted on anddismounted from an image forming apparatus main body and has a rotatedmember, wherein there is provided a driven side member having a drivenside coupling which can engage with the second intermediate couplingsection of the intermediate member having a first intermediate couplingsection(that is held on the main body side and is engaged with a drivingside coupling section connected to a driving source ) and a secondintermediate coupling section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Other objects and advantages of the present invention will becomeapparent upon reading the following detailed description and uponreference to the drawings in which:

[0087]FIG. 1 is a sectional view of a drive power transmission devicerelated to an embodiment of the invention;

[0088]FIG. 2 is an exploded perspective view of a drive powertransmission device related to an embodiment of the invention;

[0089]FIG. 3 is a diagram showing illustratively a drive powertransmission device related to an embodiment of the invention;

[0090]FIG. 4 is a diagram illustrating how a convex portion of a malecoupling section is engaged with a concave portion of a female couplingsection under a loose fitting condition;

[0091]FIG. 5(a) and FIG. 5(b) are enlarged views of a coupling sectionformed with splines;

[0092]FIG. 6(a) and FIG. 6(b) are diagrams showing relationship betweena coupling section constituting a first coupling and a coupling sectionconstituting a second coupling;

[0093]FIG. 7(a), FIG. 7(b) and FIG. 7(c) are diagrams showingillustratively various variations of a drive power transmission device;

[0094]FIG. 8 is a diagram showing an image forming apparatus relating toan embodiment of the invention;

[0095]FIG. 9 is a sectional view of a developing device;

[0096]FIG. 10 is a top view of a developing device;

[0097]FIG. 11 is a sectional view of a drive power transmission sectionof a developing device;

[0098]FIG. 12(a) and FIG. 12(b) are diagrams showing illustratively adrive power transmission device in an example of the invention; and

[0099]FIG. 13 is a graph showing vibration characteristics in an exampleof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0100] (1) Drive Power Transmission Device

[0101] A drive power transmission device relating to an embodiment ofthe invention will be explained as follows, referring to FIG. 1 and FIG.2. FIG. 1 is a sectional view of a drive power transmission devicerelated to an embodiment of the invention, and FIG. 2 is an explodedperspective view of the drive power transmission device.

[0102] In the drawing, the numeral 100 represents a driven shaftconstituting a rotated member to which a rotation from a driving sourceis transmitted. The numeral 101 is a driven side transmission memberrepresenting a driven side member that transmits a rotation to thedriven shaft 100. The driven side transmission member 101 has malecoupling section 102 formed with splines, and is fixed on the drivenshaft 100 by pin 104. Male coupling section 102 is an example of adriven side coupling.

[0103] An intermediate transmission member representing an intermediatemember is represented by 120, and it has female coupling sections 122and 124 formed with splines. Female coupling section 122 is an exampleof the second intermediate coupling, while, female coupling section 124is an example of the first intermediate coupling section.

[0104] The numeral 140 represents a driving shaft constituting a drivingsource. The numeral 142 represents a driving side transmission memberrepresenting a driving side member to which a rotation is transmittedfrom the driving shaft 140, and it has male coupling section 144 formedwith splines, and is fixed on the driving shaft 140 by pin 146. Thedriving shaft 140 constitutes the driving side.

[0105] As a material constituting driven side transmission member 101,intermediate transmission member 120 and driving side transmissionmember 142, there are used resins such as polyacetal and nylon andmetal.

[0106] Male coupling section 144 is an example of a driving sidecoupling section.

[0107] Each of the male coupling sections 102 and 144 has convexportions provided at regular intervals, namely, at regular angularintervals on a circumferential surface whose center is a rotational axisof the male coupling section, and it is preferable that the number ofthe convex portions is 4 or more. Further, female coupling section 122has concave portions engaging with the convex portions of the malecoupling section 102, namely, the concave portions are arranged atregular intervals, namely at regular angular intervals on acircumferential surface whose center is a rotational axis of the concaveportion, and it is preferable that the number of the concave portions is4 or more. In addition, female coupling section 124 has concave portionsengaging with the convex portions of the male coupling section 144, andthe concave portions are arranged, in the same way as in the malecoupling section 144, at regular intervals, namely, at regular angularintervals on a circumferential surface whose center is a rotational axisof the female coupling section, and it is preferable that the number ofthe concave portions is 4 or more. When the number of each of the convexportions and the concave portions for male coupling sections 102 and 144and for female coupling sections 122 and 124 is made to be 4 or more,occurrence of vibration caused by driving force can be repressed.

[0108] Driven shaft 100 can be coupled with and uncoupled from drivingshaft 140, and when male coupling section 102 is engaged with femalecoupling section 122 and when female coupling section 124 is engagedwith male coupling section 144, a rotation of driving shaft 140 istransmitted to driven shaft 100. The male coupling section and thefemale coupling section are engaged with each other with a play, namely,both of them are loose-fitted each other. When the driven shaft 100 ismoved in the direction toward W1, driven side transmission member 101leaves intermediate transmission member 120, and thus, the aforesaidengagement is canceled. Incidentally, the intermediate transmissionmember 120 is loosely fitted to driving shaft 140 through hole 126having a diameter slightly larger than a diameter of the driving shaft140, and is held to be capable of being displaced (capable of swinging)by stopper ring 148 that is provided on the driving shaft 140, whichprevents that the intermediate transmission member 120 comes off thedriving shaft 140.

[0109] Further, it is also possible to hold the intermediatetransmission member to be capable of being displaced with a driving sidetransmission member, a driven side transmission member, or further, amain body or an intermediate transmission member, without providing aholding member that holds an intermediate transmission member to becapable of being displaced directly on driven shaft 100 or driving shaft140. In short, the intermediate transmission member has only to beprevented from coming off when an engagement is canceled.

[0110] Various preferable modes in the present embodiment will beexplained as follows, referring to FIG. 3-FIG. 6, and these variouspreferable modes are applied to driven side transmission member 101,intermediate transmission member 120 and driving side transmissionmember 142 shown in FIG. 1.

[0111] In the present embodiment, a plurality of couplings each beingformed by engagement between a male coupling section and a femalecoupling section are provided, and these couplings are shifted in thedirection of rotational axis to make a tolerance for deviation betweenthe driving shaft and the driven shaft to be great, and thereby, aneffective buffer function is given to the drive power transmissiondevice to repress vibration on the driven side.

[0112]FIG. 3 is a diagram illustrating an arrangement wherein aplurality of couplings are arranged to be shifted in the rotational axisdirection, and it is a diagram showing illustratively the drive powertransmission device shown in FIG. 1.

[0113] In FIG. 3, coupling section A1 (corresponding to male couplingsection 144) of driving side transmission member X1 (corresponding todriving side transmission member 142) provided on a driving shaftengages with coupling section B1 (corresponding to female couplingsection 124) of intermediate transmission member X2 (corresponding tointermediate transmission member 120) to form first coupling Y1, andcoupling section A2 (corresponding to male coupling section 102) ofdriven side transmission member X3 (corresponding to driven sidetransmission member 101) provided on a driven shaft engages withcoupling section B2 (corresponding to female coupling section 122) ofintermediate transmission member X2 at second coupling Y2, and the firstcoupling Y1 and the second coupling Y2 are provided to be shifted eachother in the rotational axis direction.

[0114] In the present embodiment, the male coupling section and thefemale coupling section are engaged with each other under the loosefitting condition, namely, both of them are engaged with each other,with a play existing between them. Due to this, it is possible to makethe intermediate transmission member to have an effective bufferfunction, and vibration on the driven side is prevented.

[0115] In this case, “a play” is a half of the distance for which theintermediate transmission member can be displaced against the drivingside transmission member or against the driven side transmission memberin the direction perpendicular to the rotational axis of each of them.In the example shown in FIG. 4, the explanation about the play is asfollows.

[0116]FIG. 4 is a diagram illustrating the play provided between themale coupling section and the female coupling section in the coupling,namely, the state of engagement between a convex portion of the malecoupling section and a concave portion of the female coupling sectionunder the loose fitting condition.

[0117] In the present embodiment, when α represents a distance betweenconvex portion M1 of male coupling section A in FIG. 4 and concaveportion F1 of female coupling section B and β represents a distancebetween convex portion F2 of female coupling B and concave portion M1 ofmale coupling section A, namely, when α represents a difference betweena radius of tangential circle FC1 of the concave portion F1 and a radiusof tangential circle MC1 of the tip portion of the convex portion M1 andβ represents a difference between a radius of tangential circle FC2 ofthe convex portion F2 and a radius of tangential circle MC2 of theconcave portion M2, a value of α or β whichever smaller is a play.

[0118] Each of driving side transmission member X1 having male couplingsection A, driven side transmission member X3 and intermediatetransmission member X2 having female coupling section B is a memberformed to be cylindrical, and convex portions of the male couplingsection A and concave portions of the female coupling section B arerespectively formed on a circumference, like teeth of a gear. The playis expressed as follows, by the use of a radius of a circumference onwhich these convex portions and concave portions are formed.

[0119] When radius R of male coupling section A is assumed to representa radius of tangential circle Mc1 or MC2 of male coupling section givinga value of α or α whichever smaller, and when radius r of femalecoupling section B is assumed to represent a radius of tangential circleFc1 or FC2 of female coupling section, play ΔR is expressed by ΔR=r−R.

[0120] After experiments, it has been cleared that vibration on thedriven side can favorably be prevented when driving the driven side torotate, by making a play to be 0.08 mm or more in a small-sized drivepower transmission device as used for an image forming apparatus.

[0121] Further, it is especially preferable that a play is made to be0.2 mm or more. It is actually preferable that a play is made to be 1 mmor less.

[0122] When a play is smaller than 0.08 mm, vibration tends to be causedon the driven side. When a play is greater than 1 mm, an intermediatetransmission member is greatly inclined under the state where a drivenside transmission member is not mounted, easiness for mounting acomponent to be mounted on or dismounted from tends to be lowered. Inaddition, strength of the coupling is lowered.

[0123] In the present embodiment, strength of a drive power transmissiondevice is improved when an operating point of the coupling section islowered. This will be explained as follows, referring to FIG. 5(a). FIG.5(a) and FIG. 5(b) are enlarged views of a coupling section formed bysplines. In FIG. 5(a), convex portion M of a coupling section hasoperating surface H, and the operating surface H engages withcorresponding surface K of concave section F to transmit driving power.The operating surface in this case is a surface of the convex portion orthe concave portion on the downstream side in the rotational directionin the coupling where the coupling section of the driven side engageswith the second intermediate coupling section, and it is a surface ofthe convex portion or the concave portion on the upstream side in therotational direction in the coupling where the coupling section of thedriven side engages with the second intermediate coupling section.

[0124] Relationship between a driving side transmission member and adriven side transmission member for the driving side transmission memberand the driven side transmission member is not naturally limited to thatshown in FIG. 5(a) and FIG. 5(b), and various combinations are possible.

[0125] Incidentally, in the explanation for FIG. 5(a) and FIG. 5(b), aconvex portion forming a coupling section is called a tooth, a tipportion of the convex portion is called addendum and a root section ofthe convex portion is called dedendum.

[0126] In FIG. 5(a), operating surface H of convex portion M of acoupling section is composed of straight line section H2 representing amain operating surface, R (Rounded) section H1 of addendum and R sectionH3 of dedendum. By providing R section H1 on addendum in addition to thestraight line section H2 on the operating surface, an operating pointrepresenting an operation center of driving power on operating surface His lowered toward dedendum of the male coupling section. Due to this,strength of the coupling section is enhanced and strength of the drivepower transmission device is improved. Though the R section is providedon addendum in the example shown in FIG. 5(a), addendum has only to bechamfered for lowering the operating point, and a shape of a chamferedportion may be R, namely, other curves in a shape of an arc or astraight line.

[0127] In the present embodiment, an operating surface on the couplingsection is formed on a plane including a rotational axis. Due this,vibration on the driven side is prevented effectively. This will beexplained by referring to FIG. 5(b).

[0128] It is preferable that operating surface HA of concave portion Fof the coupling section is formed on plane HP including rotational axisPt as shown in FIG. 5(b). By forming the operating surface HA like this,operating force that is received by concave portion F acts in thedirection of a tangent on a rotational circle as shown with V1, and theoperating force has no power to displace rotational axis Pt.

[0129] On the contrary to the foregoing, when operating surface HE isnot formed on a plane including a rotational axis like concave portionsshown with E, operating force is not in the direction of a tangent on arotational circle as shown with V2, and there are generated rotationdriving force shown with V2 a for rotational axis Pt and a component offorce to displace rotational axis Pt shown with V2 b. As a result,vibration and rotation unevenness are caused.

[0130] In the present embodiment, when an expected life of a unit thatcan be mounted on and dismounted from a main body is shorter than thatof the main body, it is possible to lower the rate of troubles in thewhole of the drive power transmission device by making the safety factorof the first coupling to be different from that of the second coupling.This will be explained as follows, referring to FIG. 3.

[0131] In FIG. 3, when an expected life of a unit that can be mounted onand dismounted from a main body is shorter than that of the main body,it is preferable that the safety factor of the first coupling Y1 is madeto be different from that of the second coupling Y2, and it isespecially preferable that the safety factor of the coupling betweenintermediate transmission member X2 and driving side transmission memberX1 holding the intermediate transmission member X2 to be movable, orbetween intermediate transmission member X2 and driven side transmissionmember X3 is established to be smaller than that of the other side. Inthis case, making a safety factor to be different from the other meanschanging of the strength of the coupling, and for example, this can becarried out by changing a material, or by changing a length of thecoupling in the axial direction. Therefore, making the safety factor tobe smaller is weakening the strength of the coupling, and this can becarried out by using a material having lower strength or shortening alength of the coupling in the axial direction.

[0132] Due to this, the safety factor of the coupling of the drive powertransmission device is matched with the relationship between a life ofthe main body and that of a unit to be mounted on or dismounted from themain body that the expected life of the unit to be mounted on ordismounted from the main body is shorter than that of the main body,thus, the rate of troubles of the device can be lowered effectively.

[0133] In the present embodiment, an arrangement is made so that anoperating surface of intermediate transmission member X2 for drivingside transmission member X1 may be deviated in terms of a phase fromthat of the intermediate transmission member X2 and of the driven sidetransmission member X3. Due to this, generation of vibration caused bydriving power is prevented and vibration on the driven side isprevented.

[0134] This will be explained as follows, referring to FIG. 6(a) andFIG. 6(b). FIG. 6(a) and FIG. 6(b) show relationship between couplingsection B1 constituting first coupling Y1 in FIG. 3 and coupling sectionB2 constituting second coupling Y2. Incidentally, FIG. 6(a) showsintermediate transmission member X2 viewed in the direction of W2 inFIG. 3, while, FIG. 6(b) shows intermediate transmission member X2viewed in the direction of W3 in FIG. 3. As illustrated, the couplingsection B1 and the coupling section B2 are formed to be different interms of a phase. In the coupling section B1, recessed operating surfaceH is formed on standard line RL, while in the coupling section B2, itsphase is established so that the aforesaid recessed portion formed tohave pitch angle of 20° may have its operating surface H on line SLdeviated from the standard line by 5°.

[0135] By establishing phase relationships between the coupling sectionB5 and the coupling section B2 as stated above, the force applied fromthe driving shaft to the driven shaft is dispersed in term of progressof time, which eliminates unevenness of rotation of the driven shaft andfurther represses vibration of the driven shaft.

[0136] Next, various embodiments of the invention will be explained asfollows, referring to FIG. 7(a), FIG. 7(b) and FIG. 7(c), which arediagrams showing illustratively drive power transmission devices.

[0137] In FIG. 7(a), male coupling section A1 is provided on drivingside transmission member X1, female coupling section B is provided onintermediate transmission member X2 and male coupling section A2 isprovided on driven side transmission member X3. The female couplingsection B is engaged with the male coupling section A1 and the malecoupling section A2 in common at positions which are different inrotational axis direction W. Namely, first coupling Y1 formed by themale coupling section Al and the female coupling section B and secondcoupling Y2 formed by the male coupling section A2 and the femalecoupling section B are arranged to be deviated each other in rotationalaxis direction W.

[0138] The intermediate transmission member X2 has stopper section X4,which prevents that the intermediate transmission member X2 leaves whenthe driven side transmission member X3 is removed. The stopper sectionX4 is provided on the intermediate transmission member X2, and thestopper section X4 has a hole to which the driven side transmissionmember X3 is fitted loosely so that the intermediate transmission memberX2 may be displaced. A diameter of the hole that is larger than anoutside diameter of coupling section X1 makes the intermediatetransmission member X2 to be held on the driving side transmissionmember X1 to be capable of being displaced.

[0139]FIG. 7(b) shows the structure wherein the driving sidetransmission member X1 has female coupling section A1, male couplingsection B1 and female coupling section B2 are formed on the intermediatetransmission member X2, and the female coupling section B2 is made toengage with male coupling section A2 of the driven side transmissionmember X3, and thereby, first coupling Y1 and second coupling Y2 are notoverlapped each other in rotational axis direction W except a range of Dwhere they are overlapped partially, and thus, a tolerance of deviationbetween the driving shaft and the driven shaft is increased. In theexample shown in FIG. 7(b), coupling section A1 corresponds to malecoupling section 144 in FIG. 1, coupling section B1 corresponds tofemale coupling section 124, coupling section B2 corresponds to femalecoupling section 122 and coupling section A2 corresponds to malecoupling section 102, though relationship of correspondence between maleand female is partially different.

[0140] Incidentally, it is also possible to employ the structure whereina male coupling section is provided on the driven side transmissionmember, a female coupling section and a male coupling section areprovided on the intermediate transmission member, and a female couplingsection is provided on the driven side transmission member.

[0141]FIG. 7(c) is a diagram showing exploded first coupling Y1 andsecond coupling Y2, and it shows an arrangement example wherein aplurality of concave portions forming coupling section B of intermediatetransmission member X2 are made to engage alternately with convexportions of coupling section A1 of the driving side transmission member(not shown) provided on the driving shaft and with convex portions ofcoupling section A2 of the driven side transmission member (not shown)provided on the driven shaft, and thereby the first coupling Y1 and thesecond coupling Y2 are overlapped each other and are arranged atpositions which are deviated in the direction of rotational axis W.

[0142] (2) Image Forming Apparatus

[0143] The structure of an image forming apparatus in the embodiment ofthe invention will be explained as follows, referring to FIG. 8.

[0144] In the drawing, image forming apparatus 1 is composed ofautomatic document feeder DF, document image reader IR for reading animage on a document conveyed by the automatic document feeder DF,exposure device ED that gives exposure, in accordance with data afterimage processing, to drum-shaped photoreceptor 10 representing an imagecarrier, and of photoreceptor 10, and there are provided, around thephotoreceptor, image forming section IF including charging electrode 14representing a charging means, developing device 16 composed of adeveloping device of a magnetic brush type, transfer electrode 18representing a transfer means, separation electrode 20 representing aseparation means and cleaning device 21, and a storing section SS forsheet feeding trays 22 and 24 each storing recording sheet P. Thecharging electrode 14, the exposure device ED and the developing device16 constitute a toner image forming means that forms a toner image on animage carrier.

[0145] It is also possible to use a dielectric substance and anintermediate transfer body for the image carrier, in addition tophotoreceptor 10. It is further possible to use an electrostatic imageforming means such as a needle electrode and a screen electrode and adeveloping device for the toner image forming means stated above.

[0146] Main factors of the automatic document feeder DF include documentstand 26 and document conveyance processing section 28 that includes aroller group including roller 29 and a switching means (having nosymbols) for switching a path for movement of a document in case ofneed.

[0147] The document image reader IR is located below platen glass 27,and it is composed of two mirror units 30 and 31 capable ofreciprocating by keeping an optical path length, fixed image forminglens (hereinafter referred to simply as a lens) 33 and linear imagepick-up element (hereinafter referred to as CCD) 35.

[0148] The exposure device ED has therein laser diode 40 representing alight-emitting element, rotary polygon mirror 41 representing apolarizing means, and a driving circuit representing a driving meansthat generates pulses for driving the laser diode 40, and it is formedas a unit as illustrated.

[0149] Numeral R10, shown at this side of transfer electrode 18 whenviewed from the movement direction of recording sheet P, is aregistration roller, and one shown with the numeral 36 at the downstreamside of separation electrode 20 is a fixing device.

[0150] The fixing device 36 is composed of a roller having therein abuilt-in heating source and of a pressure-contact roller that rotateswhile being in pressure contact with the aforesaid roller.

[0151] The numeral 38 represents a cleaning means for the fixing device36, and its main factor is a cleaning web that is provided to be capableof being taken up.

[0152] When a of documents (not shown) placed on the document stand 26is passing below the roller 29 after being conveyed by the documentconveyance processing section 28, the sheet is illuminated byilluminating means 32.

[0153] Reflected light from a document passes through mirror units 30and 31 located at fixed positions and through lens 33, and it is formedon CCD 35 as an image which is then read.

[0154] Image information, obtained through reading by the document imagereader IR, are processed to be image data which are stored in a memorythat is not shown.

[0155] The image data are read out of the memory in the case of imageforming, and laser diode 40 representing a light-emitting element in theexposure device ED is driven in accordance with the aforesaid image dataread out, and thereby, photoreceptor 10 is exposed to light.

[0156] Prior to the exposure, photoreceptor 10 rotating in the arrowdirection (counterclockwise) is given a prescribed surface voltage bycorona discharge action of charging electrode 14. After the exposure,voltage on the exposed area is lowered in accordance with an amount ofthe exposure, resulting in formation of an electrostatic latent image onphotoreceptor 10 corresponding to image data.

[0157] The electrostatic latent image is subjected to reversaldevelopment conducted by developing device 16, and a toner image isformed. On the other hand, before the leading edge of the toner image onthe photoreceptor 10 arrives at the transfer area, a sheet of recordingsheets P in sheet feeding tray 22, for example, is fed out and conveyedto arrive at registration roller RIO to be regulated in terms ofposition.

[0158] Recording sheet P is conveyed toward the transfer area byregistration roller RIO that starts rotating to synchronize so that therecording sheet P may be overlapped with the toner image, namely, withthe image area on the photoreceptor 10.

[0159] In the transfer area, the toner image on the photoreceptor 10 istransferred onto the recording sheet P by charging made by transferelectrode 18, and then, the recording sheet P is separated from thephotoreceptor 10 by neutralizing made by separation electrode 20.

[0160] After that, the toner image is fused and fixed on the recordingsheet P by pressing and heating in the fixing device 36, and therecording sheet P is ejected out to sheet ejection tray 37 through sheetejection path 78 and sheet ejection roller 79.

[0161] Sheet feeding trays 22 and 24 are arranged to be on a verticaldouble decks in the present embodiment, and it is also possible toprovide more sheet trays.

[0162] There is formed space section 25 having a prescribed clearancebetween a bottom portion (same as a bottom wall in meaning) of sheetfeeding tray 24 arranged on the lower deck (which means the lowest deckin the case where the number of decks is other than two in the presentembodiment) among sheet feeding trays and the bottom wall of theapparatus main body.

[0163] The space section 25 is one to be used in the mode to form imageson both sides of recording sheet P, and it contributes to achievement ofreversing a recording sheet from obverse to reverse or vice versatogether with second conveyance path 80 for reversing a recording sheetfrom obverse to reverse or vice versa (described later).

[0164] Each of the numerals 50 and 53 shown over the tip portions(corresponding to the leading edge of recording sheet P stored whenviewed in the sheet feeding direction) of sheet feeding trays 22 and 24is a sheet feeding means (hereinafter referred to as a feed-out roller)composed of a roller, each of the numerals 51 and 54 is a feed roller,and each of 52 and 55 is a double-feed-prevention roller.

[0165] Feed-out rollers (50, 53) and feed rollers (51, 54) are unitizedto have the structure wherein both of them can easily be mounted on ordismounted from a driving shaft connected with a driving source providedon the apparatus main body side or an engagement means provided on thesheet feeding section.

[0166] Further, the double-feed-prevention rollers (52, 55) are unitizedto have the structure wherein they can easily be mounted on ordismounted from a fixed member provided at the fixing section on theapparatus main body.

[0167] The numeral 60 is a bypass sheet feeding tray in the bypass sheetfeeding section, and it is constructed so that it may be opened andclosed with its lower end functioning as the fulcrum on the main bodyside wall of image forming apparatus 1.

[0168] Numeral 61 represents a feed-out roller composed of a roller forfeeding out a recording sheet placed on the bypass sheet feeding tray 60in the course of image forming, numeral 63 represents a feed rollerprovided at the downstream side of the feed-out roller 61, and numeral65 represents a double-feed-prevention roller that is in pressurecontact with the feed roller 63, prevents double-feeding of recordingsheet P and has the structure that is essentially the same as in thecase of the sheet feeding trays 22 and 24 stated above.

[0169] A conveyance path for recording sheet P fed out of bypass sheetfeeding tray 60 is represented by 66, and the conveyance path passesthrough a pair of conveyance rollers shown on the left side of the feedroller 63, and is communicated with a junction described later.

[0170] Numeral 70 represents a first conveyance path for making imageforming by transfer to be conducted on recording sheet P, and it isextended from the bottom toward the top when viewed in the direction ofmovement of a recording sheet fed out of a concerning sheet feed tray.

[0171] A sheet feeding path for a recording sheet stored in sheetfeeding tray 22 on the upper deck is represented by numeral 72, andnumeral 74 represents a sheet feeding path for a recording sheet storedin sheet feeding tray 24 on the lower deck, while, numeral 76 representsa junction section (a part of the first conveyance path 70) whererecording sheet P conveyed from the sheet feeding tray 22 and recordingsheet P conveyed from the sheet feeding tray 24 join.

[0172] Numeral 78 is a sheet ejection path for ejecting a recordingsheet on which a prescribed image has been formed onto sheet ejectiontray 37.

[0173] Numeral 80 represents a second conveyance path for reversing arecording sheet from obverse to reverse or vice versa that is used inthe case of forming images on both sides of a recording sheet, and it iscommunicated with the first conveyance path on the upper portion in thedrawing.

[0174] The second conveyance path 80 is extended from the top to thebottom when viewed in the direction of movement of a recording sheet.

[0175] A lower end portion of the second conveyance path 80 is made tobe a conveyance path extending almost vertically, and its lower endextends to be lower than a sheet feeding portion of the sheet feedingtray 24 on the lower deck, and is connected (communicated) with thefirst conveyance path 70.

[0176] As is understood from the foregoing, the first conveyance path 70and the second conveyance path 80 form a loop shape that is long in thelongitudinal direction on the side wall of the apparatus main body.

[0177] On the connection portion where the first conveyance path 70 andthe second conveyance path 80 are connected to each other, there isprovided conveyance means R20 composed of a pair of rollers capable ofrotating reversely.

[0178] The connection portion may also be called a junction thatswitches both conveyance paths, because recording sheet P is notconveyed continuously from the second conveyance path 80 to the firstconveyance path 70.

[0179] Under roller R20 for switchback, there is provided a pathcommunicated with space section 25, and the path is used to makerecording sheet P moving through second conveyance path 80 to head forthe space section 25, when reversing recording sheet P from obverse toreverse or vice versa.

[0180] In the image forming process, an arrangement is made so that thetrailing edge of the recording sheet P is held by the roller R20 forswitchback when recording sheet P moving through the second conveyancepath 80 is fed out toward the space section 25, and therefore, a part ofthe recording sheet is stored in the space section 25.

[0181] Numeral 90 represents an (upper) branch guide, and it iscontrolled to make the recording sheet P having an image formed on itsfirst side to head for sheet ejection path 78 or for second conveyancepath 80. The branch guide 90 is controlled in accordance with asingle-side mode and a two-side mode to switch the recording sheetconveyance path.

[0182] For example, when the mode to conduct image forming on both sidesof a recording sheet is established, the branch guide 90 is located atthe position shown with broken lines in the drawing to feed recordingsheet p on which an image is formed on its first side to turn in atransferred toner image into second conveyance path 80, and afterfeeding the recording sheet into the second conveyance path 80, thebranch guide 90 is controlled through an unillustrated control sectionto take the position shown with solid lines in the drawing.

[0183] Incidentally, members (having no reference symbols) positioned onthe first conveyance path 70 and the second conveyance path 80 and areshown with a pair of circles represent conveyance rollers.

[0184] The image forming process for the second side of the recordingsheet in the image forming apparatus of the aforesaid structure is asfollows.

[0185] As stated above, when the recording sheet P having an image onits first side moves upward through the first conveyance path 70 andwhen its leading edge arrives at the branch guide 90, the branch guide90 is kept at the position shown with broken lines in the drawing.Therefore, the recording sheet P enters the second conveyance path 80and keeps moving.

[0186] An entrance portion of the second conveyance path 80 forms agentle arc which assures smooth movement of the recording sheet P.

[0187] When the recording sheet P moves downward through the secondconveyance path 80 and arrives at its lower end, the recording sheet Pis interposed by rollers R20 for switchback to be conveyed downward tocome off the second conveyance path, and is guided to space section 25formed below the lower sheet feeding tray 24.

[0188] In this case, the first side of the recording sheet P on which animage has been formed faces downward.

[0189] Then, the rollers R20 for switchback stop rotating in the statewherein the trailing edge of the recording sheet P is interposed by therollers R20 for switchback, and after that, when the rollers R20 forswitchback start rotating in the opposite direction, the recording sheetP is fed into the first conveyance path 70 under the condition that therecording sheet is reversed from inside to outside, namely, under thecondition that the second side on which an image has not been formedfaces to the photoreceptor 10 side, and the leading edge of therecording sheet P is regulated by registration roller R10.

[0190] On the other hand, on the photoreceptor 10, there is formed asecond toner image through the aforesaid process, and when registrationroller R10 starts rotating in synchronization with rotation of thephotoreceptor 10, the recording sheet P enters a transfer area to beoverlapped with the second toner image area.

[0191] After that, when the leading edge of the recording sheet P whichhas been subjected to transfer processing, separation processing andfixing processing arrives at a certain portion of the branch guide 90,the branch guide 90 is kept at the position shown with solid lines inthe drawing in advance to communicate the first conveyance path 70 withsheet ejection path 78, and communication with the second conveyancepath 80 is cut, therefore, the recording sheet P enters the sheetejection path 78 to be ejected on sheet ejection tray 37 through sheetejection roller 79. Thus, an image is formed on the recording sheet.

[0192]FIG. 9 is a sectional view of developing device 16. Inside outerframe 260 of the developing device 16, there are provided developingsleeve 210, blade wheel 220, and stirring conveyance screws 230 and 231.Inside the developing sleeve 210, there is provided fixed magnet 211,and developing agent regulating plate 212 is provided to face thedeveloping sleeve 210. Two-component developing agent including tonerand carrier is stored in the developing device, and toner suppliedthrough an unillustrated opening is stirred and conveyed by the stirringconveyance screws 230 and 231 to be supplied to the blade wheel 220, andthe blade wheel 220 that rotates in the arrowed direction supplies toneron the developing sleeve 210. The developing sleeve 210 rotates in thearrowed direction, and due to this rotation, developing agent on thedeveloping sleeve 210 is regulated by the developing agent regulatingplate 212 to be supplied to the developing position where the developingsleeve 210 faces photoreceptor 10.

[0193]FIG. 10 is a plan view of developing device 16.

[0194] Developing agents are conveyed in the white arrow direction byrotation of stirring conveyance screws 230 and 54 4581 231 and of bladewheel 220, and are supplied to developing sleeve 210.

[0195] Next, rotation drive of developing sleeve 210 and rotation driveof blade wheel 220 and of stirring conveyance screws 230 and 231 will beexplained as follows, referring to FIG. 11. In the present embodiment,developing sleeve 210, blade wheel 220 and stirring conveyance screws230 and 231 are driven respectively by different driving sources.

[0196] Developing sleeve 210 is driven to rotate by driving powertransmitted by gear 300 from an unillustrated motor. Gear 300 anddriving side transmission member 310 are fixed on driving shaft 301, andthe driving side transmission member 310 rotates integrally with gear300.

[0197] Intermediate transmission member 320 has female coupling section321, which engages with male coupling section 311 of the driving sidetransmission member 310. The intermediate transmission member 320 hasfemale coupling section 322.

[0198] Driven shaft 340 on which the developing sleeve 210 is supportedrotatably by supporting member 342 fixed on an image forming apparatusmain body through bearing 341. Male coupling section 331 of driven sidetransmission member 330 engages with female coupling section 322 ofintermediate transmission member 320.

[0199] Owing to the drive power transmission mechanism, namely, owing tocoupling between male coupling section 311 of driving side transmissionmember 310 and female coupling section 321 of intermediate transmissionmember 320 and to coupling between female coupling section 322 ofintermediate transmission member 320 and male coupling section 331 ofdriven side transmission member 330, rotation is transmitted fromdriving shaft 301 to driven shaft 340, and thus, developing sleeve 210is rotated.

[0200] Blade wheel 220 is fixed on driven shaft 440 and is rotated bydrive power transmitted to pulley 400 that is driven by an unillustratedmotor.

[0201] On driving shaft 401 on which a pulley is fixed, there is fixeddriving side transmission member 410. The driving side transmissionmember 410 has male coupling section 411, which engages with femalecoupling section 421 of intermediate transmission member 420. Theintermediate transmission member 420 has female coupling sections 421and 422, and the female coupling section 422 engages with male couplingsection 431 of driven side transmission member 430 that is fixed ondriven shaft 440 on which the blade wheel 220 is fixed. As stated above,power is transmitted from driving shaft 401 to driven shaft 440 by bothcoupling formed with male coupling section 411 of driving sidetransmission member 410 and with female coupling section 421 ofintermediate transmission member 420 and coupling formed with femalecoupling section 422 of intermediate transmission member 420 and withmale coupling section 431 of driven side transmission member 430.

[0202] Developing device 16 is detachably mounted on an image formingapparatus main body. In the driving mechanism stated above, with regardto the driving mechanism of developing sleeve 210, driven shaft 340 anddriven side transmission member 330 are provided on developing device 16which is mounted on and dismounted from the image forming apparatus mainbody, while, intermediate transmission member 320, driving sidetransmission member 310 and driving shaft 301 are provided on the imageforming apparatus main body. The intermediate transmission member 320has hole 323 that is slightly larger than a diameter of driving shaft301, and the driving shaft 301 is inserted in the hole 323 with a play.On the driving shaft 301, there is provided stopper ring 304 whichprevents the intermediate transmission member 320 from coming off theimage forming apparatus main body when the developing device 16 is takenout and the driven side transmission member 340 is removed accordingly.Namely, the intermediate transmission member 320 is movably supported onthe driving side transmission member 310.

[0203] In the driving mechanism of blade wheel 220, driven sidetransmission member 430 and intermediate transmission member 420 areprovided on developing device 16 which is mounted on and dismounted fromthe image forming apparatus main body. The intermediate transmissionmember 420 has hole 423 that is slightly larger than a diameter ofdriven shaft 440, and the driven shaft 440 is inserted in the hole 423with a play. On the driven shaft 440, there is fixed stopper ring 442which prevents the intermediate transmission member 420 from coming offwhen the intermediate transmission member 420 is taken out as a part ofthe developing device 16. Namely, the intermediate transmission member420 is movably supported on the driven side transmission member 430.

[0204] In the image forming apparatus stated above, there has been shownan example of a developing unit wherein developing device 16 is unitizedas a process cartridge capable of being mounted and dismounted, and theprocess cartridge includes the following various ones which can bemounted detachably on the image forming apparatus.

[0205] (1) Image Forming Body

[0206] An image forming body such as a photoreceptor is formed to be aprocess cartridge as an image forming body unit.

[0207] (2) Photoreceptor and Charging Electrode

[0208] A photoreceptor and a charging electrode are formed to be aprocess cartridge.

[0209] (3) Photoreceptor, Charging Electrode and Developing Device

[0210] A photoreceptor, a charging electrode and a developing device areformed to be a process cartridge.

[0211] (4) Photoreceptor, Charging Electrode, Developing Device andCleaning Device

[0212] A photoreceptor, a charging electrode, a developing device and acleaning device are formed to be a process cartridge.

[0213] (5) Color Process Cartridge

[0214] Developing devices respectively for yellow, magenta, cyan andblack are formed to be one process cartridge which is mounted on anddismounted from an image forming apparatus main body. In the processcartridge like this, there may also be incorporated a photoreceptor anda charging electrode in addition to the developing device mentionedabove.

[0215] (6) Image Holding Body

[0216] An image holding body such as an intermediate transfer body thatholds a transferred toner image temporarily is formed on a processcartridge as an image holding body unit.

[0217] (7) Intermediate Transfer Body and Another Process Section

[0218] An intermediate transfer body and at least one of processsections described in aforesaid items (1)-(5) are formed to be a processcartridge.

EXAMPLE

[0219] Vibration of the developing device of an image forming apparatuswas examined by making the developing device to be a process cartridgeand by driving a developing sleeve of the developing device to rotatewith a drive power transmission device shown in FIG. 12(a) and FIG.12(b), having the following dimensions and serving as a drive powertransmission device for a developing sleeve.

[0220] Let it be assumed that R1 represents a radius of a male couplingsection of driving side transmission member X1, r1 represents a radiusof a female coupling section of intermediate transmission member X2engaging with the aforesaid male coupling section, R2 represents aradius of a coupling section of driven side transmission member X3 andr2 represents a radius of a coupling section of the intermediatetransmission member X2 engaging with the aforesaid coupling section. Letit be assumed that L represents a distance between a first couplingbetween the driving side transmission member X1 and the intermediatetransmission member X2 and a second coupling between the driven sidetransmission member X3 and the intermediate transmission member X2, L1represents a length of the first coupling and L2 represents a length ofthe second coupling mentioned above.

[0221] In the present example, vibration of the driven side was measuredwhen the driven side was driven to rotate under the conditions ofL1=L2=6 mm, L=8 mm and ΔR=r1−R=r2−R2=0.85 mm.

[0222] Further, as a comparative example, there was used a drive powertransmission device having one step of coupling wherein radii of a malecoupling section and a female coupling section and a length of acoupling are the same as those shown in FIG. 12(a), X1 having a malecoupling section is made to be a driving side transmission member asshown in FIG. 12(b), and X3 having a female coupling section is made tobe a driven side transmission member.

[0223] As a result, vibration in the example employing two steps ofcoupling was much less than that in the comparative example employingone step of coupling composed of a male coupling and a female coupling,as shown in FIG. 13. Incidentally, vibration data shown in FIG. 13represent a value of a frequency component for one turn obtained bymeasuring with a laser displacement gage (LK 2500 made by Kyence Co.)and by conducting FFT analyses. 61 4581

[0224] Although it has been extremely difficult, in a prior art, tosufficiently repress a vibration generated on the driven side whendriving a component to be mounted or dismounted, the invention makes itpossible to repress the vibration sufficiently.

[0225] The invention makes it possible to repress a vibration on thedriven side extremely effectively.

[0226] According to the present invention, a vibration on the drivenside is repressed further favorably.

[0227] The invention prevents that an intermediate transmission memberthat accelerates vibration on the driven side comes off when the drivenside is removed.

[0228] According to the present invention, a vibration on the drivenside is repressed effectively.

[0229] In the invention, signals on the driven side are preventedextremely favorably, because an effect of power to displace a rotationalaxis of a driven side transmission member has been eliminated.

[0230] The invention makes it possible to enhance strength of a drivepower transmission device effectively. According to the presentinvention, it is possible to enhance strength of a coupling on theportion where mounting and dismounting operations are conducted.

[0231] According to the present invention, strength of a coupling can beimproved, and strength of a drive power transmission device can beimproved effectively.

[0232] According to the present invention, drive power to be transmittedfrom a driving side transmission member to a driven side transmissionmember is dispersed on a time series basis to act on the driven sidetransmission member, and therefore, vibration of the driven sidetransmission member is prevented extremely effectively.

[0233] The invention effectively prevents the vibration generatedperiodically.

[0234] The invention prevents vibration of rotary members in a cartridgethat is mounted on or dismounted from an image forming apparatus. As aresult, an image with high image quality can be formed.

[0235] The invention makes it possible to form a color image with highimage quality.

[0236] The invention makes it possible to realize a process cartridgewhich is mounted on an image forming apparatus to form an image withhigh image quality.

[0237] The invention makes it possible to realize a process cartridgewhich is mounted on an image forming apparatus to form an image withhigh image quality and offers excellent workability when mounting on ordismounting from the image forming apparatus.

[0238] The invention prevents that an intermediate transmission membercomes off when removing a process cartridge from an image formingapparatus main body.

[0239] The invention makes it possible to realize a process cartridgewhich can easily be mounted on or dismounted from an image formingapparatus main body and hardly has vibration when acting for imageforming.

[0240] Disclosed embodiment can be varied by a skilled person withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A transmission mechanism for transmittingrotation of a driving source in a main body to an object mounted on themain body for receiving the rotation, the transmission mechanismcomprising: a plurality of couplings provided at different positionsalong an axial direction of a rotating axis; wherein each of thecouplings comprises, a male coupling member having a plurality of convexelements provided at an identical interval on an outer circumferentialsurface of the rotating axis; and a female coupling member having aplurality of concave elements for engaging with the convex elements. 2.The transmission mechanism of claim 1 , wherein the object is detachablefrom the main body.
 3. The transmission mechanism of claim 1 , whereinthe male coupling member provides more than four convex elements and thefemale coupling member provides more than four concave elements.
 4. Thetransmission mechanism of claim 1 , wherein each convex elements has anaffecting surface arranged on a plane including the rotating axis, andwherein the affecting surface transmits a driving force to one of theconcave elements.
 5. The transmission mechanism of claim 1 , whereineach of stresses of the couplings is different.
 6. The transmissionmechanism of claim 1 , wherein a top corner of an affecting surface ofeach the convex elements is chamfered, and wherein the affecting surfacetransmits a driving force to one of the concave elements.
 7. Thetransmission mechanism of claim 1 , wherein each of the convex elementshas an affecting surface transmitting a driving force to one of theconcave elements, and wherein a phase of affecting surfaces of one ofthe couplings is different from a phase of affecting surfaces of anotherone of the couplings.
 8. A transmission mechanism for transmittingrotation of a driving source in a main body to a detachable bodydetachably mounted on the main body, the transmission mechanismcomprising: a driving coupling member provided in the main body, whereinthe driving coupling member is rotated by the driving source; anintermediate member having a first coupling member and a second couplingmember, both of which are provided at different positions along an axialdirection of a rotating axis; and a driven coupling member provided inthe detachable body; wherein the driving coupling member couples withthe first coupling member and the driven coupling member couples withthe second coupling member so that the rotation of the driving source istransmitted from the driving coupling member to the driven couplingmember through the intermediate member, and wherein each of the firstcoupling member and the second coupling member is either a male couplingmember or a female coupling member.
 9. The transmission mechanism ofclaim 8 , wherein the driving coupling member loosely couples with thefirst coupling member, and the driven coupling member also looselycouples with the second coupling member.
 10. The transmission mechanismof claim 9 , wherein each of plays between the driving coupling memberand the first coupling member and between the driven coupling member andthe second coupling member is more than 0.08 mm.
 11. The transmissionmechanism of claim 10 , wherein each of the plays is less than 1.00 mm.12. The transmission mechanism of claim 8 , wherein the male couplingmember has more than four convex elements, and the female couplingmember has more than four concave elements.
 13. The transmissionmechanism of claim 8 , wherein a first stress between the drivingcoupling member and the first coupling member is different from a secondstress between the second coupling member and the driven couplingmember.
 14. The transmission mechanism of claim 13 , wherein the firststress is less than the second stress in case that the intermediatemember holds to the driving coupling member, and the second stress isless than the first stress in case that the intermediate member holds tothe driven coupling member.
 15. The transmission mechanism of claim 8 ,wherein a top corner of an affecting surface of the convex element ischamfered, and wherein the affecting surface transmits a driving forceto a concave element coupling with the convex element.
 16. Thetransmission mechanism of claim 8 , wherein the first and secondcoupling members have male coupling members having a plurality of convexelements positioned at an identical interval on an outer circumferentialsurface of the rotating axis, wherein each the convex elements has anaffecting surface transmitting a driving force to a concave elementcoupling with the convex element, and wherein a phase of affectingsurfaces of one of the male coupling members is different from a phaseof affecting surfaces of the other of the male coupling members.
 17. Thetransmission mechanism of claim 8 , wherein the male coupling member hasa plurality of convex elements and the female coupling member has aplurality of concave elements, and wherein a number of the convex or theconcave elements of the first intermediate coupling member accords witha number of the convex or the concave elements of the secondintermediate coupling member.
 18. The transmission mechanism of claim 8, wherein the first coupling member or the second coupling member iscoupled with either the driving coupling member or the driven couplingmember so that the intermediate member has a variable angle to therotating axis in case that the detachable body is detached from the mainbody.
 19. A transmission mechanism for transmitting rotation of adriving source in a main body to a detachable body detachably mounted onthe main body, the transmission mechanism comprising: a driving couplingmember provided in the main body, wherein the driving coupling member isrotated by the driving source; an intermediate member having a firstcoupling member and a second coupling member, both of which are providedat different positions along an axial direction of a rotating axis; anda driven coupling member provided in the detachable body; wherein thedriving coupling member couples with the first coupling member and thedriven coupling member couples with the second coupling member so thatthe rotation of the driving source is transmitted from the drivingcoupling member to the driven coupling member through the intermediatemember, and wherein the first coupling member or the second couplingmember is coupled with either the driving coupling member or the drivencoupling member so that the intermediate member keeps its own positionloosely with some play to the rotating axis in case that the detachablebody is detached from the main body.
 20. The transmission mechanism ofclaim 19 , wherein each of the first coupling member and the secondcoupling member has either a male coupling member which has a pluralityof convex elements positioned at an identical interval on an outercircumferential surface of the rotating axis or a female coupling memberwhich has a plurality of concave elements for engaging with theplurality of convex elements.
 21. A transmission mechanism fortransmitting rotation of a driving source in a main body to a detachablebody detachably mounted on the main body, the transmission mechanismcomprising: a male coupling member provided in either the main body orthe detachable body, wherein the male coupling member has a plurality ofconvex elements provided at an identical interval on an outercircumferential surface of a rotating axis; and a female coupling memberprovided in the other of either the main body or the detachable body,wherein the female coupling member has a plurality of concave elementsfor engaging with the convex elements; wherein one of the convexelements and the concave elements provided in the main body haveaffecting surfaces for transmitting a driving force to the other of theconvex elements and the concave elements provided in the detachablebody, and wherein each top corner of the affecting surfaces ischamfered.
 22. A process cartridge, detachably mounted on a main body ofan image forming apparatus, to which rotation of a driving source,located at the main body, is transmitted, the process cartridgecomprising: an intermediate member having a first coupling membercoupled with a driving coupling member rotated by the driving source,and having a second coupling member, wherein the first and secondcoupling members are provided at different positions along an axialdirection of a rotating axis; a driven coupling member coupled with thesecond coupling member, wherein the rotation of the driving source istransmitted from the driving coupling member to the driven couplingmember through the intermediate member; wherein each of the firstcoupling member and the second coupling member is either a male couplingmember or a female coupling member.
 23. A process cartridge, detachablymounted on a main body of an image forming apparatus, to which rotationof a driving source, located at the main body, is transmitted, theprocess cartridge comprising: an intermediate member having a firstcoupling member coupled with a driving coupling member rotated by thedriving source, and having a second coupling member; a driven couplingmember coupled with the second coupling member, wherein the rotation ofthe driving source is transmitted from the driving coupling member tothe driven coupling member through the intermediate member; wherein thesecond coupling member is coupled with the driven coupling member sothat the intermediate member keeps its own position loosely with someplay to a rotating axis in case that the process cartridge is detachedfrom the main body.
 24. An image forming apparatus comprising: a mainbody providing a driving source; an object mounted on the main body; atransmission mechanism for transmitting rotation of the driving sourcefrom the main body to the object, wherein the transmission mechanism hasa plurality of couplings provided at different positions along an axialdirection of a rotating axis, and wherein each of the couplingscomprises, a male coupling member having a plurality of convex elementsprovided at an identical interval on an outer circumferential surface ofthe rotating axis; and a female coupling member having a plurality ofconcave elements for engaging with the convex elements.
 25. The imageforming apparatus of claim 24 , wherein the object comprises a processcartridge detachably mounted on the main body.
 26. An image formingapparatus comprising: a main body providing a driving source; adetachable body detachably mounted on the main body; a transmissionmechanism for transmitting rotation of a driving source from the mainbody to the detachable body, wherein the transmission mechanismcomprises, a driving coupling member provided in the main body, androtated by the driving source; an intermediate member having a firstcoupling member and a second coupling member, both of which are providedat different positions along an axial direction of a rotating axis; anda driven coupling member provided in the detachable body; wherein thedriving coupling member couples with the first coupling member and thedriven coupling member couples with the second coupling member so thatthe rotation of the driving source is transmitted from the drivingcoupling member to the driven coupling member through the intermediatemember; wherein each of the first coupling member and the secondcoupling member is either a male coupling member or a female couplingmember.
 27. The image forming apparatus of claim 26 , wherein thedetachable body comprises a process cartridge.